In the past, numerous devices have been utilized in identifying two or more points on a horizontal plane. Such devices have been used to assure that the foundation for a home is level, to properly place a suspended ceiling, to lay a level concrete floor, swimming pool, sewer line, landscape, deck, fence, bridge and other structures which are intended to be level.
In the surveying industry there are sophisticated optical scopes and electronic levels available, however these items are quite costly, cumbersome and difficult to operate. In the carpentry industry it is seldom practical or financially feasible to justify the acquisition of these tools. In this field, the prior art included the utilization of a clear plastic tube having an inner diameter of approximately 1/4 inch, which is partially filled with water. In establishing a level for a suspended ceiling, opposite ends of the tube would be held by two workers. A reference point would be established at one point along the ceiling. One worker would hold the tube so that the water level in the tube would be aligned with this reference point. This is known as the reference end of the tube. The other worker, at what is known as the working end of the tube, would mark points around the room, which would also align with the water level. Since water seeks its own level, all marked points around the room would be level with the reference point. It should be noted that in order to accomplish this function, two separate workers are required, each being at opposite ends of the tube.
Where only one worker was available, it was known in the prior art that the tube utilized could be marked with tape at the working end, at the level of the reference point. The procedure would be as follows. Firstly, one end of the tube would be affixed to a wall with the water level aligned with the reference point. This would, of course, be the reference end of the tube. Secondly, a piece of tape, or other marking, would be placed at the corresponding level of water at the working end of the tube. Thirdly, the sole carpenter would then identify points around the room where the water level would reach the tape on the working end of the tube. A level area would thus be located. There were shortcomings with this approach in that if any water inadvertently spilled out, a corresponding degree of inaccuracy would be achieved. Also, if throughout operations, there were temperature changes effectuated, for example, by sunlight, the volume of fluid would expand or contract and thereby adversely affect the accuracy of the results.
Also known to the prior art were line levels which involved stretching lines around the perimeter and across the area to be levelled. The taut lines would be levelled by use of the bubble type spirit line levels. The taut lines were not without disadvantages. They were quite inaccurate; were difficult to use in that lines would be placed in many locations; they required two individuals to operate, one to look at the line level and the other to adjust the end of the line; and finally, they were not of universal application because they could only operate to the extent of the one's line of sight, as they could not be used to negogiate corners or go under passageways.
It would appear advantageous to provide a levelling device which is accurate, inexpensive, durable, simple to operate, not adversely affected by temperature changes, capable of functioning around corners, through or under passageways beyond one's line of sight, and which can be operated by one worker.